text: The development of electron spectroscopy can be considered to have begun in 1887 when the German physicist Heinrich Rudolf Hertz discovered the photoelectric effect but was unable to explain it. In 1900, Max Planck (1918 Nobel Prize in Physics) suggested that energy carried by electromagnetic waves could only be released in "packets" of energy. In 1905 Albert Einstein (1921 Nobel Prize of Physics) explained Planck's discovery and the photoelectric effect. He presented the hypothesis that light energy is carried in discrete quantized packets (photons), each with energy hν to explain the experimental dobservations. Two years after this publication, in 1907, P. D. Innes recorded the first XPS spectrum.
  After numerous developments and the Second World War, Kai Siegbahn (Nobel Prize in 1981) with his research group in Uppsala, Sweden registered in 1954 the first XPS device to produce a high energy-resolution XPS spectrum. In 1967, Siegbahn published a comprehensive study of XPS and its usefulness, which he called electron spectroscopy for chemical analysis (ESCA). Concurrently with Siegbahn's work, in 1962, David W. Turner at Imperial College London (and later Oxford University) developed ultraviolet photoelectron spectroscopy (UPS) for molecular species using a helium lamp.